import java.util.LinkedList;
import java.util.ListIterator;

/** Let's implement a stack using a LinkedList.
 */
public class LinkedListStack implements StackInterface
{
  private LinkedList list;

  public LinkedListStack()
  {
    list = new LinkedList();
  }

  public void push(Object o)
  {
    System.out.println("pushing " + o);
    list.add(o);
  }

  public Object pop()
  {
    Object victim = peek();
    list.remove(list.size() - 1);
    System.out.println("popping " + victim);
    return victim;
  }

  public Object peek()
  {
    return list.get(list.size() - 1);
  }

  public int size()
  {
    return list.size();
  }

  // We want to show the top (end) of the stack on top, so the iterator
  // starts at size.  The parameter we pass to listIterator() starts the
  // iterator point to the element that would be returned if we call next.
  public String toString()
  {
    StringBuilder build = new StringBuilder();

    ListIterator iter = list.listIterator(list.size());
    while(iter.hasPrevious())
    {
      build.append("\t" + iter.previous() + "\n");
    }
    return build.toString();
  }
}